And this is where it gets to social bonding. That vagus is linked to the regulation of the muscles in the face and the head. So that when individuals have more facial expressivity and even the intonation of their voices, are actually reflecting how that newer mammalian vagus is working. So in many ways, we wear our heart on our face, and we project our heart in our voice. And so, people have always said...if you understand, literally, the evolutionary history of mammals, they were using voice to signal to other that they were safe. Voices weren't words, they were vocalizations, and vocalizations had intonation. And if the intonation had melodic tones, it was basically signaling that their visceral state was safe to come to.
So now, what the Polyvagal Theory basically proposed and discussed, was that the autonomic nervous system, the nervous system that regulates our visceral, our bodily state, is actually composed of several stages from our evolution. So it's phylogenetic stages, and as we evolved to become mammals, newer stages were added. And those stages had different adaptive properties. So the ancient or the very old vagal circuit, if it recruited for reaction to environments, shut us down, but when used in a homeostatic way for health, it supports digestion, guts, and all those other good stuff.
Then we had a sympathetic nervous system that came on with other vertebrates, and that helped us mobilize to fight or flee. And most people in psychology think of that as the only defense system, but it's not. It's actually a newer defense system. And this ancient defense system of shutting down is really good for reptiles, but literally very dangerous for mammals, because we need oxygen. Again, if you look at people who have gone through trauma, they've shut down, and our nervous system never evolved to switch easily from immobilization to a normal social behavior.
Then with mammals, we had a newer autonomic nervous system, which was a new myelinate vagus to the navel. That vagal system could calm and to shut down sympathetic, so it calms from fight or flight. And that one was wired to the muscles of the face and head. Social behavior became part of the regulation of physiological state. So social behavior became the way that we identified another person as being safe. And we as mammals evolve not to function as an isolate, we evolve to be taken care of when we're young, and to have friends and mates when we're older. And one of the functions of those others in our lives is to help us regulate our physiology. So that's the long answer of your short question.
So now, what the Polyvagal Theory basically proposed and discussed, was that the autonomic nervous system, the nervous system that regulates our visceral, our bodily state, is actually composed of several stages from our evolution. So it's phylogenetic stages, and as we evolved to become mammals, newer stages were added. And those stages had different adaptive properties. So the ancient or the very old vagal circuit, if it recruited for reaction to environments, shut us down, but when used in a homeostatic way for health, it supports digestion, guts, and all those other good stuff.
Then we had a sympathetic nervous system that came on with other vertebrates, and that helped us mobilize to fight or flee. And most people in psychology think of that as the only defense system, but it's not. It's actually a newer defense system. And this ancient defense system of shutting down is really good for reptiles, but literally very dangerous for mammals, because we need oxygen. Again, if you look at people who have gone through trauma, they've shut down, and our nervous system never evolved to switch easily from immobilization to a normal social behavior.
Then with mammals, we had a newer autonomic nervous system, which was a new myelinate vagus to the navel. That vagal system could calm and to shut down sympathetic, so it calms from fight or flight. And that one was wired to the muscles of the face and head. Social behavior became part of the regulation of physiological state. So social behavior became the way that we identified another person as being safe. And we as mammals evolve not to function as an isolate, we evolve to be taken care of when we're young, and to have friends and mates when we're older. And one of the functions of those others in our lives is to help us regulate our physiology. So that's the long answer of your short question.
